What is a requirement for an adult to be considered competent in making medical decisions?

For an adult to be considered competent in making medical decisions, they must understand the implications of their choices. Competence in this context refers to the individual's ability to comprehend the information related to their medical situation, including the potential risks and benefits of the proposed treatments or procedures. This understanding allows them to make informed decisions that align with their values and preferences.

The other options do not adequately address the primary criterion for decision-making competency. Prior medical experience is not necessary for a patient to make informed choices about their health; rather, the capacity to understand and process relevant information is the critical factor. Completing a healthcare consent form is important, but it is a procedural step, not a definitive indicator of understanding or competence. Lastly, age alone does not determine competency; individuals younger than 21 can also be competent if they possess the requisite understanding of their medical situation.